The present invention relates to optical scanning devices and more particularly to a portable scanning device for generating a scan pattern which retains the same configuration in space throughout the scanning volume.
In the present-day merchandising point-of-sale checkout systems, data pertaining to the purchase of a merchandise item is obtained by reading data encoded indicia such as a bar code label printed on or attached to the purchased merchandise item. Reading systems which have been constructed to read this type of bar code include stationary optical scanning systems normally located within the cabinet structure of a checkout counter or hand-held bar code scanners which emit a single or multiple line scan pattern which are manually moved pass the bar code label that is to read. Where a hand-held bar code scanner is utilized in scanning a bar code label, it has been found that the distance between the laser scanner and the bar code label is critical in locating the scan pattern on the label. As the distance between the scanner and the label increases, the scan pattern becomes larger but the intensity of the scan pattern is reduced which presents problems in targeting a scan pattern on the bar code label. It would be desirable to have the center of the scan pattern remain at the same intensity regardless of the distance of the bar code label from the scanner which would enhance the correct positioning of the scan pattern on the bar code label thereby increasing the percentage of good read operations occurring during a checkout operation.